Power over Ethernet (PoE) is a technique for providing electrical power over an Ethernet network cable, typically in combination with also providing a network data connection over the same Ethernet network cable. Two Institute of Electrical and Electronics Engineers (IEEE) 802.3 standards provide details of standardized implementations of PoE, IEEE 802.3af-2003 (also referred to herein as 802.3af) and IEEE 802.3at-2009 (also referred to herein as 802.3at), with the 802.3at standard providing for higher power transmission and additional power management techniques as compared to the original 802.3af standard. Collectively or individually, the IEEE 802.3af and 802.3at standards may also be referred to herein as Standard PoE.
For PoE implementations, equipment that provides power to other devices over an Ethernet cable is referred to as Power Sourcing Equipment (PSE) or a Power Sourcing Equipment device (PSE device). A PSE device compliant with IEEE 802.3af and/or 802.3at standards may be referred to herein as a Standard PSE. Commonly used PSE devices are PoE compliant switches, which can provide power to various devices connected to the Ethernet ports of the switch over a twisted pair network cable. A PSE device which is a switch may be referred to herein as an endpoint or endspan. Endpoint devices typically include AC/DC power supplies for converting AC voltage as might be provided by, for example, an electrical outlet in the United States, to the DC voltages employed by PoE.
For networks which do not employ PoE switches, intermediary devices can be used to inject power onto an Ethernet cable so that one or more devices may be powered from the intermediary device. Such an intermediary device may be referred to herein as a midspan device or midspan injector. Midspan injectors are, commonly, devices that plug into AC line power or an AC/DC converter and have two network ports, one port for data communication with a network device, such as a switch, hub, or router, and another port that provides data and power to devices that consume power provided from the midspan injector. Midspan devices sit between Powered Devices and network communication devices, such as switches, hubs or routers, to inject power onto the Ethernet cable without disrupting the data also being transported over the cable.
A device that is powered by a PSE device is referred to herein as a Powered Device (PD). A PD compliant with IEEE 802.3af and/or 802.3at standards may be referred to herein as a Standard PD. Various network devices can be implemented as a PD. Commonly encountered PDs include Internet Protocol (IP) telephones, also referred to as Voice Over IP (VOIP) phones, IP video cameras, IEEE 802.11 compliant wireless access points, repeaters, and bridges, other network appliances, such as routers, firewalls, and other security appliances, and various access control systems. Virtually any electrical or network device, however, can be implemented as a PD, provided the device's power requirements are suitable for PoE. For example, thin clients and kiosks can be implemented as PDs and various sensors and controllers can be implemented as PDs. Certain client devices, such as computers, smart phones, and printers, may also be enabled as a PD.
For suitable devices that are not manufactured as a PoE compliant PD, a PoE splitter can be used to convert the single PoE data and power connection to separate data and power connections. In this way a PoE splitter is a type of PD itself. Such a device may appear similar to a midspan injector, with two network ports and a single power port. One network port will receive the PoE connection and separated data and power connections can then be passed to a non-PoE device to separately provide a data connection and a DC power connection.
Prior to establishment and adoption of IEEE 802.3af and 802.3at, various vendors established their own propriety methods for simultaneously transmitting power and data over a single Ethernet cable. Cisco Systems was one vendor that established a solution used by many early PD manufacturers. These pre-802.3af PoE techniques are referred to herein collectively and/or individually as Legacy systems. PDs that were compliant with a pre-standard proprietary PoE solution, but not an IEEE 802.3af and/or 802.3at standard, are referred to herein as Legacy Powered Devices (Legacy PDs). Legacy PDs are still common in the market today, so most Standard PSE devices support Legacy PDs while also being compliant with the IEEE PoE standards.